In recent years, vigorous research and development have been conducted on organic EL elements, since they emit light with a high luminance at a low driving voltage. In general, the organic EL element is constituted by opposed electrodes having sandwiched therebetween a light-emitting layer or a plurality of organic layers including a light-emitting layer, in which element electrons injected from a cathode and holes injected from an anode are recombined in the light-emitting layer to generate excitons which emit light or which transports energy to other molecules to generate light-emitting excitons. The thus-emitted light is utilized.
An invention relating to a phosphorescent light-emitting organic EL element using a metal complex as a host material has been disclosed (see JP-A-2002-305083). In Examples of this patent literature, tris (8-hydroxyquinoline) aluminum complex (Alq) is used as an electron transporting material, and an aluminum complex layer, called HB-1 in this patent literature, is sandwiched as a hole-blocking layer between a light-emitting layer and an electron transporting layer (Alq layer). Thus, light-emitting efficiency and durability of the element are still insufficient and, therefore, development of an element showing a high luminance and a high light-emitting efficiency and having an excellent durability has been eagerly demanded.